The voltage applied to the voltage coil of a wattmeter must not exceed the voltage rating of that coil.
Your question should read "How do you get a negative potential?", for the reasons explained below.The term, 'voltage', is another word for 'potential difference'. The terms 'positive' and 'negative', when applied to a potential difference or voltage indicates the sense (or direction) in which the potential difference or voltage is acting. For example, if a second voltage is acting in the same direction as another voltage then it is acting in the positive sense; if it is acting in the opposite direction then in is acting in the negative sense'.It's very important to understand that you cannot apply 'positive' and 'negative' is the sense of charge or polarity to potential difference or voltage. You can, however, apply these terms to 'potential'. Potential is relative, and always measured with respect to a given point (often, the earth). So a point can be, for example, +5 V or -5 V with respect to another point (usually earth or ground, but not necessarily).Never confuse 'potential' with 'potential difference' and remember that 'voltage' means potential difference notpotential.So, to obtain a negative potential, earth (ground) the positive terminal of the battery or d.c. supply. All potentials measured relative to earth are now negative. To obtain a positive potential, earth the negative terminal of the battery or d.c. supply instead. All potentials measured relative to earth are now positive.If you want to get a negative potential,Earth the positive terminal of the DC power sourceConnect a resistor in series with the negative terminal of the sourceAt the other end of the resistor you get a negative potential (the value's less than the value of the power supply)
Answer for USA, Canada and countries running a 60 Hz supply service.A three wire system uses two lines L1 and L2 and a Neutral. You can obtain a 120 volt potential from L1 to N or 120 volt potential from L2 to N. Between L1 and L2 you can obtain a potential of 240 volts.
You don't use any high-voltage 'lead' to provide 120 V. To obtain a 240/120-V supply from a three-phase transformer, one of the transformer's secondary 240-V windings has a grounded centre tap which provides the neutral point. The potential difference across the entire winding is then 240 V, while the potential difference between either end and the centre tap is 120 V.
The phantom loading is that no external load is connected in actual sense and the current and pressure coils are connected seperatly so that it will consume only less power. In this connection the voltage across pressure coil will be supply voltage even if the variac is in minimum position. CONNECTION Connect a single phase supply through a single phase variac. Connect the currect coil of wattmeter M and energy meter c1 and an ammeter in series to phase terminal of singlephase variac. The pressure coil of both wattmeter and energymeter should be shorted and connected to phase of supply (not to the variac). The terminal V of wattmeter and p2, c2 of energy meter should be connected to neutral terminal of variac. PROCEDURE Keeping the variac in minimum position and switch on supply. Adjust the variac to get different reading in ammeter and note the time for 5 Revolution of energy meter disc and obtain the wattmeter reading. FORMULAE %error = (R.E - A.E)*100/A.E , WHERE, R.E is the recorded energy = n/N (n=5 & N=energymeter const.) A.E is the actual energy A.E= (wattmeter reading*time)/(3600*1000) while plotting a error graph it will be having a zig-zag shape. Normally the error can be upto 10%
The phantom loading is that no external load is connected in actual sense and the current and pressure coils are connected seperatly so that it will consume only less power. In this connection the voltage across pressure coil will be supply voltage even if the variac is in minimum position. CONNECTION Connect a single phase supply through a single phase variac. Connect the currect coil of wattmeter M and energy meter c1 and an ammeter in series to phase terminal of singlephase variac. The pressure coil of both wattmeter and energymeter should be shorted and connected to phase of supply (not to the variac). The terminal V of wattmeter and p2, c2 of energy meter should be connected to neutral terminal of variac. PROCEDURE Keeping the variac in minimum position and switch on supply. Adjust the variac to get different reading in ammeter and note the time for 5 Revolution of energy meter disc and obtain the wattmeter reading. FORMULAE %error = (R.E - A.E)*100/A.E , WHERE, R.E is the recorded energy = n/N (n=5 & N=energymeter const.) A.E is the actual energy A.E= (wattmeter reading*time)/(3600*1000) while plotting a error graph it will be having a zig-zag shape. Normally the error can be upto 10%. Winston Netto SSET-SCMS Engineering college.
Make sure that the test meter is on the correct voltage scale. Place one lead on one of the conductors to be tested and the other lead on the other voltage source conductor. The reading you obtain will be the voltage potential between the two conductors.
To measure voltage in a circuit, the voltmeter should be connected in parallel across the component or portion of the circuit where the voltage is to be measured. Ensure the voltmeter is set to the appropriate voltage range before making the connection. It is important to place the voltmeter correctly to obtain an accurate voltage reading without affecting the circuit's operation.
A coil.
There is not enough information to answer this question correctly. As the current increases through a diode, the voltage dropped across it increases. This correlation is not a linear function such as a resistance, and a datasheet for the diode or a curve tracer would be necessary to obtain the correct function. To explain further, if there were 25 series LEDs all with a 3 volt drop across them, a 75 volt potential would be measured across the diodes, and 45 volts would be measured across the 5000 ohm resistor. Ohms law will show that 45 volts applied to 5K ohms will equal 9mA. This violates the 20mA criteria in the question.
Ask the potential employer for one.
This can only be done using a voltage regulator.
using voltage controlled oscillator